What looks like spatters from an oil leak, sped through west Michigan corn fields like a bullet train and packed a wallop like a 10-pound hammer to corn yields? In the summer of 2018, the answer was corn tar spot. Never heard of it? If you raise corn, you need to learn about it.

Of course, not every field in Michigan was impacted by corn tar spot, but those that were left a notable impression on growers that were facing severe lodging, poor test weights and substantially reduced yields this fall in the wake of this disease. Dairy producers were also hard hit, with heavily infected corn silage fields drying down much quicker than normal, making it difficult to pack silage, reducing feed quality and yields. There were several reports of 40 to 50 bushel per acre reductions in corn grain yields on normally highly productive fields.

Martin Chilvers, Michigan State University field crops pathologist, says that corn tar spot, a fungal disease caused by the pathogen Phyllachora maydis,was first found in Michigan in Allegan County in 2016, and in the U.S. in 2015. Since that time, the disease has spread widely through west and Mid-Michigan by 2018. The disease is common in Mexico and other Latin American countries.

What partially makes the pathogen unique is the stealthy nature of the infection. Symptoms of the initial infection are subtle, but it must spread quickly and quietly through the plant. By the time most growers noticed significant leaf symptoms, the stands began to collapse, usually in late August or early September.

The Chilvers Lab was able to do some preliminary work looking at the effectiveness of some common fungicide options available for use on corn in August of 2018. Chilvers was also able to use the MSU Michigan Corn Variety Test Plots to evaluate disease severity on varieties submitted to the trials. He will be sharing these results and providing valuable insights on how best to scout for and manage this disease at upcoming Pest Management Update meetings held throughout Michigan during January and February 2019.

These Pest Management Update meetings will run from 9 a.m.-2:30 p.m. and MSU Extension specialists and educators will present new information about pest management research and practices in field crops. Each meeting will cover the same information. The cost is $30 per person with lunch provided as well as a free copy of the MSU Extension bulletin E0434, “2019 Weed Control Guide for Field Crops.”